Activity、Fragment和Surface的生命周期

这里首先推荐大家一本Android的学习书籍：《第一行代码》，这本书还是写得非常好的。好了，进入正题，我们先来了解一下Activity、Fragment的的生命周期中经历的几个阶段。

Activity	Fragment

下面我们假设有如下的场景，Activity内部有一个Fragment，Fragment内部是一个SurfaceView。
分为两种情况，一种是在资源文件直接加载Fragment标签，例如：

<Fragment
        android:name="com.myapplication.MainFragment"
        android:id="@+id/main_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

另一种是动态加载Fragment，先在资源文件定义存放Fragment的容器，然后通过FragmentTransaction:add()和FragmentTransaction:commit()函数创建并加载，例如：

<FrameLayout
        android:id="@+id/main_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

测试代码如下：

Activity

public class MainActivity extends AppCompatActivity implements  {
    private MainFragment mMainFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        LogUtils.init(0, ILog.LEVEL_INFO, "magnity", null);

        LogUtils.i("activity onCreate enter");

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mMainFragment = (MainFragment)getSupportFragmentManager().
                findFragmentById(R.id.main_content);
        if (mMainFragment == null) {
            mMainFragment = MainFragment.newInstance();
            getSupportFragmentManager().beginTransaction().
                    add(R.id.main_content, mMainFragment).commit();
        } 

        LogUtils.i("activity onCreate leave");
    }

    @Override
    protected void onStart() {
        LogUtils.i("activity onStart enter");
        super.onStart();
        LogUtils.i("activity onStart leave");
    }

    @Override
    protected void onResume() {
        LogUtils.i("activity onResume enter");
        super.onResume();
        LogUtils.i("activity onResume leave");
    }

    @Override
    protected void onPause() {
        LogUtils.i("activity onPause enter");
        super.onPause();
        LogUtils.i("activity onPause leave");
    }

    @Override
    protected void onStop() {
        LogUtils.i("activity onStop enter");
        super.onStop();
        LogUtils.i("activity onStop leave");
    }

    @Override
    protected void onDestroy() {
        LogUtils.i("activity onDestroy enter");
        super.onDestroy();
        LogUtils.i("activity onDestroy leave");
    }
}

Fragment

public class MainFragment extends Fragment {
    public MainFragment() {
        // Required empty public constructor
    }

    public static MainFragment newInstance(String param1, String param2) {
        MainFragment fragment = new MainFragment();
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        LogUtils.i("fragment onCreate enter");
        super.onCreate(savedInstanceState);
        LogUtils.i("fragment onCreate leave");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        LogUtils.i("fragment onCreateView enter");
        View v = inflater.inflate(R.layout.fragment_main, container, false);
        LogUtils.i("fragment onCreateView leave");
        return v;
    }

    @Override
    public void onAttach(Context context) {
        LogUtils.i("fragment onAttach enter");
        super.onAttach(context);
        LogUtils.i("fragment onAttach leave");
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        LogUtils.i("fragment onActivityCreated enter");
        super.onActivityCreated(savedInstanceState);
        LogUtils.i("fragment onActivityCreated leave");
    }

    @Override
    public void onStart() {
        LogUtils.i("fragment onStart enter");
        super.onStart();
        LogUtils.i("fragment onStart leave");
    }

    @Override
    public void onResume() {
        LogUtils.i("fragment onResume enter");
        super.onResume();
        LogUtils.i("fragment onResume leave");
    }

    @Override
    public void onPause() {
        LogUtils.i("fragment onPause enter");
        super.onPause();
        LogUtils.i("fragment onPause leave");
    }

    @Override
    public void onStop() {
        LogUtils.i("fragment onStop enter");
        super.onStop();
        LogUtils.i("fragment onStop leave");
    }

    @Override
    public void onDestroyView() {
        LogUtils.i("fragment onDestroyView enter");
        super.onDestroyView();
        LogUtils.i("fragment onDestroyView leave");
    }

    @Override
    public void onDestroy() {
        LogUtils.i("fragment onDestroy enter");
        super.onDestroy();
        LogUtils.i("fragment onDestroy leave");
    }

    @Override
    public void onDetach() {
        LogUtils.i("fragment onDetach enter");
        super.onDetach();
        mListener = null;
        LogUtils.i("fragment onDetach leave");
    }
}

SurfaceView

public class MainSurfaceView extends SurfaceView implements SurfaceHolder.Callback {
    public MainSurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        getHolder().addCallback(this);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        LogUtils.i("surface surfaceCreated");
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        LogUtils.i("surface surfaceChanged");
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        LogUtils.i("surface surfaceDestroyed");
    }
}

打印结果

动态加载
启动应用并加载MainActivity，打印如下：

activity onCreate enter
activity onCreate leave
activity onStart enter
fragment onAttach enter
fragment onAttach leave
fragment onCreate enter
fragment onCreate leave
fragment onCreateView enter
fragment onCreateView leave
fragment onActivityCreated enter
fragment onActivityCreated leave
fragment onStart enter
fragment onStart leave
activity onStart leave
activity onResume enter
activity onResume leave
fragment onResume enter
fragment onResume leave
surface surfaceCreated
surface surfaceChanged

按HOME键切到后台，打印如下：

activity onPause enter
fragment onPause enter
fragment onPause leave
activity onPause leave
surface surfaceDestroyed
activity onStop enter
fragment onStop enter
fragment onStop leave
activity onStop leave

恢复到前台，打印如下：

activity onStart enter
fragment onStart enter
fragment onStart leave
activity onStart leave
activity onResume enter
activity onResume leave
fragment onResume enter
fragment onResume leave
surface surfaceCreated
surface surfaceChanged

退出MainActivity，打印如下：

activity onPause enter
fragment onPause enter
fragment onPause leave
activity onPause leave
surface surfaceDestroyed
activity onStop enter
fragment onStop enter
fragment onStop leave
activity onStop leave
activity onDestroy enter
fragment onDestroyView enter
fragment onDestroyView leave
fragment onDestroy enter
fragment onDestroy leave
fragment onDetach enter
fragment onDetach leave
activity onDestroy leave

静态加载
启动应用并加载MainActivity，打印如下：

activity onCreate enter
fragment onAttach enter
fragment onAttach leave
fragment onCreate enter
fragment onCreate leave
fragment onCreateView enter
fragment onCreateView leave
activity onCreate leave
activity onStart enter
fragment onActivityCreated enter
fragment onActivityCreated leave
fragment onStart enter
fragment onStart leave
activity onStart leave
activity onResume enter
activity onResume leave
fragment onResume enter
fragment onResume leave
surface surfaceCreated
surface surfaceChanged